[Minimal Residual Disease (MRD) in gastric carcinoma--an overview]

Despite recent developments in therapy for gastric cancer, the prognosis of this disease remains poor in advanced stages. In many cases even curatively treated patients without any residual tumour develop metachronous metastases. As in other solid tumours, adjuvant therapies can reduce the metastatic risk, which implies that some of these patients harbour isolated tumour cells or micrometastases (minimal residual disease, MRD) that are undetectable by radiological imaging and conventional histopathology but can still be the cause of tumour recurrence. Therefore, reliable methods for diagnosing MRD would be desirable for individually tailoring therapy for these patients. Unfortunately, testing methods for MRD and interpretation of their results are not standardised and studies published on this topic are difficult to interpret due to methodological differences and small sample sizes. As of now, testing for MRD has not become relevant in clinical routine for any of the anatomic compartments lymph nodes, peritoneal lavage fluid, peripheral blood, and bone marrow in the Western hemisphere. Most reliable data on MRD in gastric cancer patients have been reported for peritoneal lavage fluid. In some centres in Japan, this test is routinely being used for making therapeutic decisions, e. g., on the use of intraperitoneal chemotherapy. MRD in resected lymph nodes will be further evaluated in the context of the sentinel lymph node concept and possibly be employed for designing individualised therapy for patients in early disease stages who are not routinely candidates for multimodal treatment. As for tumour cells in peripheral blood and in bone marrow, studies suggest that these cells are only able to form metastases in the presence of certain molecular factors. Therefore, rather than simply confirming the existence of isolated tumour cells in blood or bone marrow, future studies should concentrate on defining their molecular characteristics and the conditions required for their metastatic potential. This may gain relevance in diagnostics and prognostic evaluation of individual patients as well as in the development of targeted therapies directly interfering with the metastatic process.